1. Field of the Invention
The present invention relates to a lead frame comprising a plurality of mounting portions on which semiconductor elements are mounted, a manufacturing method thereof, a semiconductor apparatus, and a method of manufacturing the semiconductor apparatus.
2. Description of the Related Art
Recently, accompanying down-sizing of semiconductor packages, there is an increasing number of semiconductor packages having a leadless structure that are manufactured according to a batch sealed assembly method. According to the batch sealed assembly method, a pattern corresponding to a plurality of semiconductor elements is arranged on a single lead frame, respective semiconductor elements are mounted and bonded thereon, and thereafter the plurality of semiconductor elements are sealed together in one batch using a sealing resin material. In this assembly method, after the semiconductor elements are sealed with a resin material, the lead frame is divided by dicing to obtain single semiconductor elements as individual pieces.
For example, as shown in FIG. 1, lead frame 104 of this type includes a plurality of mounting portions 111 on which semiconductor elements are mounted, a plurality of electrodes 112 to which respective semiconductor elements are electrically connected, and corner portions 113 that connect the plurality of mounting portions 111. Corner portion 113 has a plurality of hanging lead pieces 115 that support mounting portion 111, and electrode connection piece 116 that connects the plurality of electrodes 112. As shown in FIG. 2, in corner portion 113 that comprises lead frame 104, a plurality of electrode connection pieces 116 are formed to intersect at the center part of corner portions 113 in a cross shape.
Further, as shown in FIG. 3, as the corner portion of another lead frame related to the present invention, Japanese Patent Laid-Open No. 2002-26190 (FIG. 7) discloses annular corner portion 123 in which a plurality of hanging lead pieces 115 and a plurality of electrode connection pieces 116 are connected to form a quadrilateral shape.
As shown in FIG. 4, to obtain a so-called anchor effect which is a favorable bonding state using sealing resin material 106, lead frame 104 related to the present invention that is usable with the above described batch sealed assembly method is formed with concave portion 117 in the thickness direction of lead frame 104 by performing a half-etching process at a plurality of places such as the side of outer circumference of mounting portions 111, hanging lead pieces 115, or electrode connection pieces 116. Therefore, a lead frame related to the present invention is, in general, formed by an etching process. This leads to an increase in manufacturing cost.
Next, a method of manufacturing a semiconductor package related to the present invention that uses lead frame 104 in which concave portion 117 is formed by an etching process will be briefly described.
According to the method of manufacturing a semiconductor package related to the present invention, as shown in FIG. 5 semiconductor elements 103 are mounted on mounting portions 111 of lead frame 104, and semiconductor elements 103 and electrodes 112 are electrically connected through wires 105. Subsequently, as shown in FIG. 6A, a plurality of semiconductor elements 103, electrodes 112, wires 105, and a surface on one side of lead frame 104 are covered and sealed with sealing resin material 106. Finally, as shown in FIG. 6B, lead frame 104 that is covered with sealing resin material 106 is cut at corner portions 113 to divide lead frame 104 into individual semiconductor packages 101.
According to a semiconductor package manufactured as described above, when the dimension of a side of the outer shape of a square semiconductor package is formed to be less than 3 mm, the number of semiconductor elements arranged on a single lead frame is comparatively large. Therefore, even when a lead frame formed by an etching process is used, the manufacturing cost can be made comparatively small. However, particularly in the case of a comparatively large semiconductor package in which the dimension of a side of the outer shape of a semiconductor package is formed to be 3 mm or more, the number of manufactured semiconductor packages per lead frame is comparatively small, and therefore the manufacturing cost increases. Therefore, it is desirable to decrease the manufacturing cost by using press working as the lead frame manufacturing process.
In adopting press working as the manufacturing process for half-etching processing as described above, the lead frame is subjected to a crushing process using a metal mold or the like. In the crushing process, stress and strain arises in the lead frame. Accordingly, in the case of a structure having a relatively large number of places to undergo a crushing process, such as a lead frame used in a batch sealed assembly method, the stress and strain, produced by the crushing process, accumulates. There is thus the problem that the lead frame warps significantly and changes shape. Consequently, it has been difficult to adopt press working as the manufacturing process for lead frames.
In general, performing the so-called half blanking process is considered a countermeasure that reduces stress and strain that constitutes a problem when a concave portion in a lead frame is formed by a crushing process. In the half blanking process, in addition to forming a concave portion in the thickness direction of the lead frame, a protrusion corresponding to the concave portion is also formed to reduce stress and strain that arises in the lead frame. Generally, in the case of a crushing process, stress and strain is produced over the entire area that is being crushed. In contrast, in the case of a half blanking process, because stress and strain only arises at boundary portions of the half blanking process, the amount of stress and strain is comparatively small.
However, even when half blanking on a lead frame is performed, in the case of a lead frame that is used with a batch sealed assembly method, a lead frame for a plurality of semiconductor packages is linked at places that are subject to the half blanking process. Consequently, stress that occurs in the half blanking process, is conveyed from the side of the mounting portion, that occupies a comparatively large area in the lead frame via the hanging lead pieces, to concentrate at a center portion where the hanging lead pieces intersect at the center of the corner portion, and a force that reacts to the stress, acts towards the center of the mounting portion.
Accordingly, in a lead frame, when four corner portions are arranged around a square mounting portion, the forces react to the stress come from the four corner portions that are concentrated in the center of the mounting portion. Therefore, it has not been possible to prevent the mounting portion of the lead frame from changing shape due to these forces react to the stress.
In the structure of the corner portion of the lead frame also disclosed in aforementioned Japanese Patent Laid-Open No. 2002-26190, there are locations where hanging lead pieces and electrode connection pieces are perpendicularly connected. Consequently, there is the problem that stress that arises when a half blanking process is performed is not favorably dispersed, and the forces react to the stress concentrate at the mounting portion and deformation of the mounting portion can not be prevented.
Accordingly, it has been difficult to form a lead frame which can be used with a batch sealed assembly method by press working in a process for manufacturing a semiconductor package related to the present invention.